1.Field of the Invention
The present invention relates to the field of removing blisters from a conduit. More particularly the present invention relates to the field of using a train apparatus for removing blisters from an underground fibrous conduit.
2. Description of the Prior Art
For many years, especially between the years of 1930 and 1960, and to some extent in the 1970's, a special type of conduit has been used to house underground electrical power cables. This special conduit is a fibrous duct made of wooden pulp impregnated with coal tar. The two most common interior diameters with which the ducts have been created are 4 inches interior diameter and 5 inches interior diameter. Over the years many such conduits have deteriorated and blisters have been built up in many of the underground ducts. The blisters extend for as much as 1 inch into the interior from the sidewalls of the ducts. The blisters formed in the interior of the ducts create a big problem for power network maintenance because the blisters block the openings in the ducts and prohibit cables from being placed through the ducts. In addition, the blisters squeeze existing cables. Although newer conduits have been made of plastic which do not have this problem, there are a lot of deteriorated fibrous conduits still buried underground. It is necessary to repair such conduits and remove the blisters, since it is cost prohibitive to remove all of these ducts out of the ground and replace them.
The blisters built up inside the power cable conduit made of fibrous material such as wood, create a major problem in maintaining and reconstructing existing residential houses and commercial buildings. Since the fibrous ducts are buried underground, it is hard to detect which portion of a duct has deteriorated with most blisters. The only practical solution is to dredge a large length of duct at once to remove all the blisters which have built up inside the duct. The average length of such power cable conduits is about one thousand feet. It is desirable to have a cleaning tool which can be pulled through the ducts by a cable, strong enough to scrape off the blisters, yet flexible enough to go through the twists and turns of the ducts.